Detecting or measuring the temperature of a battery, such as a lithium-ion (Li-ion) battery, may include driving an alternating current with a varying frequency into the battery, measuring a complex impedance of the battery at each frequency of the current in order to detect the frequency at which an imaginary part of the impedance is zero, and detecting the temperature based on this frequency at which the imaginary part of the impedance is zero. This method, which is known as ZIF (Zero Intercept Frequency) method is based on the fact that the imaginary part of the battery impedance is dependent on the temperature in such a way that at a given temperature the imaginary part of the battery impedance of batteries of a certain type intercepts zero at essentially the same frequency. This frequency where the imaginary part of the impedance intercepts zero is referred to as ZIF. Usually, the ZIF of a certain battery type is the higher the lower the temperature is. For each battery type the ZIF can be detected at different known temperatures (by the battery manufacturer, for example) and each of these known temperatures can be associated with a respective ZIF so as to obtain a plurality of ZIF-temperature pairs. At an application site of the battery, the temperature can be detected by detecting the ZIF, wherein the temperature is the temperature associated with the detected ZIF.
In some types of batteries, such as high quality automotive batteries, the ZIF, especially at high temperatures, may occur at relatively low frequencies. Measurements at low frequencies, however, may be affected by noise (interferences) such as interferences generated by an electric motor in an automobile. Such interferences may make measurements at low frequencies less reliable than measurements at higher frequencies.
Another approach, which is referred to as NZIF (Non Zero Intercept Frequency), is to detect those frequencies where the imaginary part of the battery impedance equals a predefined value different from zero. Each of these frequencies is associated with a certain temperature so that, similar to the ZIF method, the temperature can be detected by detecting the frequency where the imaginary part of the battery impedance equals the predefined value. A frequency where the imaginary part intercepts the predefined value different from zero is referred to as NZIF. The predefined value can be selected such that the NZIFs are higher than the ZIFs so that interferences are less likely to occur in the NZIF method. The NZIF method, however, requires a precise detection or measurement of the imaginary part of the battery impedance in order to detect when the imaginary part equals the predefined value.
Further, in both the ZIF method and the NZIF method, measurements at a plurality of different frequencies are required. This is time consuming.
There is therefore a need for an improved sensor-less battery temperature detection.